The invention relates to fluid-operated devices and, more particularly, to a valve arrangement including a release valve for controlling a fluid-operated device.
A cylinder assembly is a typical fluid-operated device. Generally, the cylinder assembly includes a cylinder having first and second ports and slideably housing a piston for movement between extended and retracted positions to move a load. To control movement of the piston and the load, a valve assembly is provided in fluid communication with a source of fluid pressure and with one or both of the ports of the cylinder assembly. The valve assembly may include a locking valve which operates to control movement of the piston upon interruption of the source of fluid pressure.
In one construction, a single locking valve is in fluid communication with one port and controls movement of the piston upon interruption of a source of fluid pressure to only that port. In another construction, a locking valve is fluidly connected to each port, and each locking valve operates independently to control movement of the piston upon interruption of the source of fluid pressure supplied to the corresponding port. In either construction, the locking valve operates to maintain the piston and the load supported by the cylinder assembly in a relatively stationary position after the interruption of the source of fluid pressure.
To release the fluid pressure from the system after operation of a locking valve, a release valve may be incorporated into the valve assembly. An example of such a release valve is disclosed in U.S. Pat. No. 4,838,306.
One of the problems with the above-described valve arrangement having a single locking valve and a single release valve connected to one port of the cylinder assembly is that, when the release valve is operated to release the fluid pressure from the system, the piston moves relative to the cylinder, and, therefore, the load also moves.
One problem with the above-described valve arrangement having a locking valve and a release valve connected to each port is that each release valve operates independently, allowing the position of the piston and the load to drift as fluid pressure is released from the system.
Another problem with the above-described valve arrangement having a locking valve and a release valve connected to each port is that, because each release valve is operated independently, an operator has difficulty simultaneously operating each release valve and maintaining the load in a relatively stationary position.
A problem with designing a release valve which controls the release of fluid pressure from both ports, simultaneously, is that, during operation of the valve assembly and during operation of the release valve, the release valve must prevent each locking valve connected to the corresponding port from being in fluid communication with the other locking valve.
The present invention provides a valve arrangement including a release valve that alleviates the problems with the above-described valve arrangements. The release valve is easy to operate and controls the release of fluid pressure from the first and second ports to maintain the position of the piston and to thereby prevent drifting of the load.
Specifically, the present invention provides a valve arrangement for controlling movement of a piston of a cylinder assembly upon interruption of a source of fluid pressure supplied to the cylinder assembly, the cylinder assembly including a first port and a second port and slideably housing the piston for movement between an extended position and a retracted position. The valve arrangement comprises a valve assembly in fluid communication with the source of fluid pressure and with the first port and the second port to control fluid flow between the source of fluid pressure and the first port and between the source of fluid pressure and the second port, and a release valve fluidly connected to the first port and to the second port, the release valve being operable to control flow of fluid from the first port and from the second port.
The valve assembly may have a valve body including a valve bore in fluid communication with the source of fluid pressure and with the first port and the second port. Preferably, the release valve includes a release valve body, defining a release valve bore in fluid communication with the valve bore and a release valve seat. The release valve also preferably includes a release valve member movable between a closed position, in which the release valve member engages the release valve seat to prevent fluid flow through the release valve bore, and an open position, in which fluid flows from the first port and the second port, through the valve bore and through the release valve bore. The release valve preferably further includes a biasing member biasing the release valve member to the closed position.
Preferably, when the release valve member is in the open position, fluid flows from the both the first port and the second port simultaneously. In addition, when the release valve member is in the open position, a substantially equal amount of fluid preferably flows from the first port and from the second port.
The release valve preferably further includes a release plunger operable to move the release valve member to the open position. Preferably, a manually engageable portion is connected to the release plunger and is engageable by an operator to cause the release plunger to move the release valve member to the open position. The release valve may include a piston portion connected to the release plunger, and a pilot fluid pressure applied to the piston portion may cause the release plunger to move the release valve member to the open position.
The release valve may also include means for biasing the release plunger out of engagement with the release valve member. In one construction, the biasing means may include a biasing member biasing the release plunger out of engagement with the release valve member. In another construction, the biasing means includes a piston portion connected to the release plunger, and a pilot fluid pressure applied to the piston portion biases the release plunger out of engagement with the release valve member. In either construction, the manually engageable portion is engageable by the operator to overcome the biasing force of the biasing member or the pilot fluid pressure to cause the release plunger to move the release valve member to the open position.
The valve assembly may include a first valve having a first valve body including a first valve bore in fluid communication with the source of pressure and the first port, and a second valve having a second valve body including a second valve bore in fluid communication with the source of fluid pressure and the second port. Preferably, the release valve bore is in fluid communication with the first valve bore and with the second valve bore, and, when the release valve member is in the open position, fluid flows from the first port, through the first valve bore, and through the release valve bore and fluid flows from the second port, through the second valve bore, and through the release valve bore.
In such constructions, when the release valve member is in the open position, fluid preferably flows from both the first valve bore and the second valve bore simultaneously. Also, when the release valve member is in the open position, a substantially equal amount of fluid preferably flows from the first valve bore and from the second valve bore.
The release valve body may further define a first release valve seat between the first valve bore and the release valve bore. The release valve preferably further includes a first release valve member movable between a closed position, in which the first release valve member engages the first release valve seat to prevent fluid flow between the first valve bore and the release valve bore, and an open position, in which fluid flows between the first valve bore and the release valve bore. A biasing member preferably biases the first release valve member to the closed position.
Similarly, the release valve body may further define a second release valve seat between the second valve bore and the release valve bore. The release valve preferably further includes a second release valve member movable between a closed position, in which the second release valve member engages the second release valve seat to prevent fluid flow between the second valve bore and the release valve bore, and an open position, in which fluid flows between the second valve bore and the release valve bore. A biasing member also preferably biases the second release valve member to the closed position.
The valve arrangement may include a flow control valve in fluid communication with the valve assembly to control fluid flow to the source of fluid pressure from at least one of the first port and the second port.
In some constructions, as discussed above, the valve assembly includes a first valve in fluid communication with the source of fluid pressure and the first port and a second valve in fluid communication with the source of fluid pressure and the second port. Preferably, the first and second valves cooperate such that, when fluid is supplied to the first port, fluid flows from the second port to allow the piston to move between the extended position and the retracted position and such that, when fluid is supplied to the second port, fluid flows from the first port to allow the piston to move between the extended position and the retracted position.
Preferably the valve arrangement further includes a cooperating plunger member positioned between the first valve and the second valve. The cooperating plunger member is operable to move the first valve member to the open position when fluid is supplied from the source of fluid pressure to the second port and to move the second valve member to the open position when fluid is supplied from the source of fluid pressure to the first port. Preferably, a biasing assembly biases the cooperating plunger member to a neutral position, in which the cooperating plunger member does not move the first valve member to the open position and does not move the second valve member to the open position.
One advantage of the present invention is that, when the release valve is operated to release fluid pressure, the piston is not allowed to move so that the load is maintained in a substantially stationary position.
Another advantage of the present invention is that, because the release valve simultaneously controls fluid flow from the first and second ports, the load does not drift when the release valve is operated.
Yet another advantage of the present invention is that, because a single release valve releases fluid pressure simultaneously from the first and second ports, the release valve is easier to operate to maintain the piston and the load in the substantially stationary position.
A further advantage of the present invention is that the release valve prevents the first and second valves from being in fluid communication during operation of the valve arrangement and during operation of the release valve.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims and drawings.